Prohovski won the semi-final in the weight category up to 80 kilograms with a unanimous decision of the judges over the Czech Adam Kan.
The native of Daugavpils was free in the first two rounds, but in the quarter-finals he beat Australian Malakji Folima, the referee stopping the fight already in the first round.
In the fight for the U-19 champion title, Prokhovskis will meet the host Elaija Lugo on Friday.
In the weight category up to 70 kilograms, Artūrs Vaišlia experienced a loss in the first fight, while Nikolaj Zamyatins and Emmanuel Sidorenko in the weight categories up to 60 and 65 kilograms were successful in the first fights, but lost in the quarter-final stage.
The U-19 World Championship in the city of Pueblo, Colorado is taking place under the supervision of the World Boxing Union (“World Boxing”) established last year.